For the first couple of games, Boston looked old and injured, with Philly’s aggressive defense forcing improvisation and a lot of missed shots.

In Game 3, Boston got their groove back. From 2008.

Boston attacked the paint early with post ups, Kevin Garnett could not miss a turnaround jumper on his way to 27 points (on just 17 shots) and Boston blew the game open in the second and third quarters in its way to an easy 107-91 win. Boston now leads the series 2-1.

Boston came out with a new aggressiveness and level of energy at both ends for this game. As veteran teams can do. Philly, a young team learning to play at this level, seemed taken aback by the new level of intensity. That is their task if they want to keep pushing Boston — the Sixers have to match that level, and they have to play better on the defensive end again. Boston shot 51.9 percent on the night and 45.5 percent from three and they will win every time if that happens.

This game was different from the opening tip, with both teams flowing better on offense. But after a couple games where Boston spent more time in the Rajon Rondo-led improvisational Celtics offense that Doc Rivers calls “random,” Boston got into their sets and into the paint early and often in Game 3.

“We (established ourselves in the post) the right way, I thought we did it through execution,” Rivers said after the game on an interview broadcast on NBA TV. “We did it through space. I thought in the first two games we tried to do it, but we did it out of random, and our spacing was poor. (Tonight) we also did it through posting the ball early, we posted Paul (Pierce 24 points on 17 shots) up early and we posted Kevin up early. And that’s the right way to play. That’s who we are. Now the shots have to go in, that makes you better. But at least the shots were the shots we wanted rather than the ones, because our offense was so poor, that we had to take. I thought that was the big difference.”

Pierce really set the tone at the end of the first quarter when the guy dragging around a leg with a sprained knee for a couple games drove and threw down two dunks, one over Thaddeus Young.

But Philly still had the lead 33-28 after one quarter as they matched Boston shot for shot. In the second the Celtics got back to playing their kind of defense — the Sixers had just 16 points in the second quarter. Boston had 32. It was an 11 point lead for Boston at the half (KG and Pierce each had 17 points already) and Philly scored just 17 in the third quarter as the game became a laugher.

This game was the best energy and aggressiveness Boston had played with this series. Philly, a young team learning to play at this level, seemed taken aback by the new level of intensity.

Rondo was impressive all night and had 23 points and 13 assists. Mikhail Pietrus knocked down some threes and had 13 off the bench. Philly’s stars struggled with Andre Iguodala taking just six shots while the previously hot Evan Turner was 1-10. The bright spot was Young coming off the bench for 22.

The two questions for Game 4 is can Boston keep this up — the energy level yes but the shooting likely cools off some — and can the Sixers raise their game to match? Game 4 is not likely to be a blowout like this gain, but it’s not going to return all the way to grind-it-out Game 2 either. The Sixers are going to have to adapt